Monitored Anesthesia Care (MAC) anesthesia is the commonly used anesthetic technique consisting of delivering drugs into the bloodstream in combination with local anesthetic infiltration by the surgeon at the operative site. MAC anesthesia is often used in combination with regional anesthesia, such as spinals, epidurals, and peripheral nerve blocks, which also provide temporary loss of feeling and movement at the operative site. The risk of using MAC anesthesia is that upper airway obstruction may occur due to respiratory depression.
During surgery, respiratory depression can occur in any person whose level of consciousness is decreased due to sedation from MAC anesthesia. Respiratory depression in the unconscious person is the result of the loss of tonicity of the submandibular muscles, which provide direct support of the tongue and indirect support to the epiglottis. As a result of this loss of tonicity, posterior displacement of the tongue may occlude the airway at the level of the pharynx, and the epiglottis may occlude the airway at the level of the larynx. The basic technique for opening the airway is the head-tilt with anterior displacement of the mandible (chin-lift or jaw-thrust maneuver).
Thus, to prevent airway obstruction, the anesthetist must achieve proper airway positioning in the patient to maintain airway patency. To this end, the anesthetist will first attempt the chin lift maneuver, which consists of manually lifting the chin upwards. This maneuver provides maintenance of proper head tilt and anterior displacement of the mandible resulting in proper alignment of the airway structures, which contributes to patient air exchange. Another option is the jaw-thrust maneuver, which is performed by placing one's hands at both sides of the mandible laterally and thrusting the jaw forward. Both methods require the anesthetist to support the patient's head manually throughout the duration of the surgery.
In some MAC anesthesia cases, an oropharyngeal or nasopharyngeal airway may be necessary to maintain airway patency. An oropharyngeal airway is a plastic, disposable, semi-circular shaped device that, when in proper position, will hold the tongue away from the posterior wall of the pharynx. However, even with the use of this device, proper head position must be maintained using either the chin-lift or jaw-thrust maneuver to keep the airway patent. indicated when the insertion of the oral airway is technically difficult or if the oral airway provides only partial relief of the airway obstruction. The airway is lubricated with a water-soluble lubricant and gently inserted close to the midline along the floor of the nostril into the posterior pharynx behind the tongue. Again, it is important to maintain head-tilt with anterior displacement of the mandible by chin-lift and, if necessary, jaw thrust when using the oropharyngeal or nasopharyngeal airway.
Surgical procedures using MAC anesthesia can range from fifteen minutes to as long as two hours. The anesthetist must continuously administer sedative medications and, assess patient response to those medications, as well as monitor and document vital signs on the patient's chart. If the anesthetist must physically perform the chin lift maneuver throughout the duration of the procedure in order to maintain patency of the airway, the additional responsibilities of monitoring, documentation, and medication administration become more cumbersome. Additionally, other factors, such as the position of the patient, often make the performance of the chin-lift maneuver awkward and inhibit the anesthetist from performing his/her other responsibilities.
In some cases, when it is obvious that maintaining continuous pressure on the mandible will be too taxing upon the anesthesia provider, he or she will choose to use general anesthesia instead of MAC anesthesia to anesthetize the patient. General anesthesia carries the risk of major complications including death, myocardial infarction, and stroke, and it also is associated with less serious complications such as vomiting, sore throat, headache, shivering, and delayed return to normal mental functioning. Thus, the disadvantages of the current methods of manually preventing airway obstruction and maintaining airway patency include:                (a) The anesthetist's movement may be restricted as a result of maintaining contact with the patient's mandible at all        (b) The anesthetist is impeded in the task of performing his or her other tasks, such as delivering medications and charting vital signs during surgery as a result of being forced to maintain continuous physical contact with the patient's mandible at all time. This results in a less efficient and more laborious performance of additional responsibilities.        (c) Factors such as operating room table placement and patient positioning can make it difficult to maintain constant upward pressure on the chin during long procedures.        (d) The anesthetist may become unnecessarily fatigued and/or stiff as a result of laboriously maintaining constant pressure upon the patient's chin.        (e) If the process of maintaining the proper head position during a MAC case becomes too laborious due to the aforementioned reasons, the anesthesia provider may choose to induce general anesthesia to alleviate these difficulties, which results in increased risk to the patient such as sore throat, increased nausea, and injury to teeth.        